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author | jack <[email protected]> | 2024-06-14 13:13:15 -0600 |
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committer | jack <[email protected]> | 2024-06-14 13:13:15 -0600 |
commit | d343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa (patch) | |
tree | 96df922dae2a5073d9a50ea70c7aae6aa37e3ebe /max_sum_circular_subarr.c | |
download | leetcode-d343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa.tar.gz leetcode-d343a3b18dbaca9297d4f7b2280c4a16f0a5c8aa.zip |
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Diffstat (limited to 'max_sum_circular_subarr.c')
-rw-r--r-- | max_sum_circular_subarr.c | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/max_sum_circular_subarr.c b/max_sum_circular_subarr.c new file mode 100644 index 0000000..85db07c --- /dev/null +++ b/max_sum_circular_subarr.c @@ -0,0 +1,46 @@ +// 918. Maximum Sum Circular Subarray +#include <stdio.h> +#define MAX(a, b) (((a) > (b)) ? (a) : (b)) + +/* + * given: circular int array 'nums' of length 'n', return the max possible + * sum of non-empty subarray of 'nums' + * + * a circular array means the end of the array connects to the beginning. + * formally, the previous element of 'nums[i]' is 'nums[(i -/+ 1) % n]' + * + * a subarray may only include each element of the fixed buffer 'nums' at + * most once. formally, for a subarray 'nums[i], nums[i + 1], ..., nums[j]' + * there does not exist i <= k1, k2 <= j with k1 % n == k2 % n + */ + +int helper(int *a, int n) { + // kadane's dp algorithm + // [https://medium.com/@rsinghal757/kadanes-algorithm-dynamic-programming-how-and-why-does-it-work-3fd8849ed73d] + int currMax, sum; + sum = currMax = a[0]; + for (int i = 1; i < n; i++) { + currMax = MAX(a[i], currMax + a[i]); + sum = MAX(currMax, sum); + } + return sum; +} + +int maxSubarraySumCircular(int *nums, int numsSize) { + int k1, k2, total = 0; + k1 = helper(nums, numsSize); + for (int i = 0; i < numsSize; i++) { + total += nums[i]; + nums[i] *= -1; + } + k2 = helper(nums, numsSize); + int ans = total + k2; + return (ans > k1 && ans != 0) ? ans : k1; +} + +int main() { + int nums1[] = {1, -2, 3, -2}, nums2[] = {5, -3, 5}, nums3[] = {-3, -2, -3}; + printf("%d\n", maxSubarraySumCircular(nums1, 4)); // expect: 3 + printf("%d\n", maxSubarraySumCircular(nums2, 3)); // expect: 3 + printf("%d\n", maxSubarraySumCircular(nums3, 3)); // expect: 3 +} |